Design and Control of a Hydraulic Power Take-Off for the ISWEC

Hydraulic power take-offs are nowadays among the first choices in power conversion systems for wave energy converters, mainly due to the high torques at stake, the low frequencies that characterise the prime mover motions and the power management achievable thanks to the implementation of accumulators and rectification valves. This work revolves around the implementation of a hydraulic power take-off on the ISWEC, a wave energy converter that exploits the gyroscopic effect on a spinning flywheel carried inside the hull to generate power from the waves. The main focus resides in the control of the transmission, an essential tool necessary to achieve consistent levels of power production in all the possible sea conditions. Two different control strategies are tested on the device. The former is a proportional control that aims at keeping the pressures as constant as possible so as to optimally tune the PTO reaction torque onto the prime mover. The latter is a customised declutching control that decouples the prime mover from the PTO when its speed is below a defined threshold, in order to let it freely accelerate and gain energy. This allows to extract power only when enough kinetic energy is available and eventually increase the overall productivity of the device. Eventually, the design of a test rig is carried out, following a design procedure established thanks to a series of analyses conducted on the transmission parameters.